1. Field of Invention
The present invention generally relates to a method for eliminating the far-end echo signal and the near-end crosstalk signal by using the echo canceller and the near-end crosstalk canceller, and more particularly, to a method for hardware reduction in the echo canceller and the near-end crosstalk canceller to achieve the objective of eliminating the far-end echo signal and the near-end crosstalk signal.
2. Description of Related Art
The transceiver is generally used in the communication system for signal transmission. The transceiver is composed of the transmitter (TX) and the receiver (RX). FIG. 1 schematically shows a full duplex transceiver with a hybrid circuit. The full duplex transceiver comprises a near-end transceiver 102 and a far-end transceiver 104. The full duplex transceiver means the send and receive operations can be operated simultaneously. The near-end transceiver 102 comprises a sender 106 and a receiver 108, and the far-end transceiver 104 comprises a sender 110 and a receiver 112. A cable 114 is connected between the near-end transceiver 102 and the far-end transceiver 104. Moreover, the near-end transceiver 102 couples to a hybrid circuit 116, the far-end transceiver 104 couples to a hybrid circuit 118. The near-end transceiver 102 and the hybrid circuit 116 are integrated into a chip, wherein the chip is generally called a communication integrated circuit (IC) used for digital signal process (DSP). Similarly, the far-end transceiver 104 and the hybrid circuit 118 are also integrated into a chip. How the full duplex transceiver transmits the signal is described in detail hereinafter.
Generally speaking, the sender 106 in the near-end transceiver 102 sends the signal to the receiver 112 in the far-end transceiver 104 via the cable 114. Similarly, the sender 110 in the far-end transceiver 104 also sends the signal back to the receiver 108 in the near-end transceiver 102. However, when the sender 106 in the near-end transceiver 102 sends the signal to the far-end transceiver 104, if the impedance of the cable 114 does not match with the impedance of the far-end transceiver 104, a far-end echo signal 120 is generated. The far-end echo signal 120 is subsequently sent back to the receiver 108 in the near-end transceiver 102, and the receiver 108 treats the far-end echo signal 120 as an interfered noise. In order to eliminate the far-end echo signal 120, an echo canceller (EC) is used. FIG. 2 schematically shows a conventional EC. The EC generally adopts an adjustable finite impulse response (FIR) filter. In FIG. 2, (X0, X1, X2, X3, . . . , XN) is an input data list, the blocks (202, 204, 206, 208 to 210) are the delay circuits to delay the input data list, C1, C2, C3, C4 to CN are the factors, and (Z0, Z1, Z2, Z3, . . . , ZN) is an output data list of the EC, where the output data list is used to eliminate the far-end echo signal. Since the transmission distance of the far-end echo signal 120 is about two times of the length of the cable 114, in order to eliminate the far-end echo signal 120 that is transmitted over such a long distance, the conventional EC has a huge number of the taps.
Furthermore, if the signal sent from the sender 106 in the near-end transceiver 102 is sent by using more than one wire, the crosstalk effect needs to be considered. In the crosstalk effect, the near-end crosstalk (NEXT) is considered as the most serious one. As shown in FIG. 1, the near-end crosstalk signal 122 generated from the crosstalk effect can be eliminated by using the near-end crosstalk canceller (NC), and the structure of the conventional NC is the same as the one shown in FIG. 2. Therefore, the conventional NC also has a huge number of the taps.
In summary, the conventional EC and NC occupy a big portion of the silicon area due to the huge number of the taps they have, so it makes the chip size very big.